[RFC PATCH] clockevents: re-calculate event when cpu enter idle

[Leo Yan]

We observed the redundant interrupts for broadcast timer, pls see
below flow:

1. Process A starts a hrtimer with 100ms timeout, then Process A will
   wait on the waitqueue to sleep;
2. The CPU which Process A runs on will enter idle and call notify
   CLOCK_EVT_NOTIFY_BROADCAST_ENTER, so the CPU will shutdown its local
   and set broadcast timer's next event with delta for 100ms timeout;
3. After 70ms later, the CPU is waken up by other peripheral's interrupt
   and Process A will be waken up as well; Process A will cancel the hrtimer
   at this point, kernel will remove the timer event from the event queue
   but it will not really disable broadcast timer;
4. So after 30ms later, the broadcast timer interrupt will be triggered
   even though the timer has been cancelled by s/w in step 3.

To fix this issue, this patch will check the situation when the cpu
enter and exit idle. So every time iterate the related cpus to calculate
the correct broadcast event value.

Signed-off-by: Leo Yan <leoy at marvell.com>
---
 kernel/time/tick-broadcast.c | 56 +++++++++++++++++++++++++++++++++++++-------
 1 file changed, 48 insertions(+), 8 deletions(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 64c5990..1dfe08e 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -679,6 +679,30 @@ static void broadcast_move_bc(int deadcpu)
 	clockevents_program_event(bc, bc->next_event, 1);
 }
 
+static void tick_broadcast_oneshot_get_earlier_event(void)
+{
+	struct clock_event_device *bc;
+	struct tick_device *td;
+	ktime_t now, next_event;
+	int cpu, next_cpu = 0;
+
+	next_event.tv64 = KTIME_MAX;
+
+	/* iterate all expired events */
+	for_each_cpu(cpu, tick_broadcast_oneshot_mask) {
+
+		td = &per_cpu(tick_cpu_device, cpu);
+		if (td->evtdev->next_event.tv64 < next_event.tv64) {
+			next_event.tv64 = td->evtdev->next_event.tv64;
+			next_cpu = cpu;
+		}
+	}
+
+	bc = tick_broadcast_device.evtdev;
+	if (next_event.tv64 != KTIME_MAX)
+		tick_broadcast_set_event(bc, next_cpu, next_event, 0);
+}
+
 /*
  * Powerstate information: The system enters/leaves a state, where
  * affected devices might stop
@@ -717,17 +741,32 @@ int tick_broadcast_oneshot_control(unsigned long reason)
 		if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
 			WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
 			broadcast_shutdown_local(bc, dev);
+
+			/*
+			 * We only reprogram the broadcast timer if we did not
+			 * mark ourself in the force mask; If the current CPU
+			 * is in the force mask, then we are going to be woken
+			 * by the IPI right away.
+			 */
+			if (cpumask_test_cpu(cpu, tick_broadcast_force_mask))
+				goto out;
+
 			/*
-			 * We only reprogram the broadcast timer if we
-			 * did not mark ourself in the force mask and
-			 * if the cpu local event is earlier than the
-			 * broadcast event. If the current CPU is in
-			 * the force mask, then we are going to be
-			 * woken by the IPI right away.
+			 * Reprogram the broadcast timer if the cpu local event
+			 * is earlier than the broadcast event;
 			 */
-			if (!cpumask_test_cpu(cpu, tick_broadcast_force_mask) &&
-			    dev->next_event.tv64 < bc->next_event.tv64)
+			if (dev->next_event.tv64 < bc->next_event.tv64) {
 				tick_broadcast_set_event(bc, cpu, dev->next_event, 1);
+				goto out;
+			}
+
+			/*
+			 * It's possible the cpu has cancelled the timer which
+			 * has set the broadcast event at last time, so
+			 * re-calculate the broadcast timer according to all
+			 * related cpus' expire events.
+			 */
+			tick_broadcast_oneshot_get_earlier_event();
 		}
 		/*
 		 * If the current CPU owns the hrtimer broadcast
@@ -802,6 +841,7 @@ int tick_broadcast_oneshot_control(unsigned long reason)
 			 * the cpu local timer device.
 			 */
 			tick_program_event(dev->next_event, 1);
+			tick_broadcast_oneshot_get_earlier_event();
 		}
 	}
 out:
-- 
1.9.1